Autoionization and ultrafast relaxation dynamics of highly excited states in N2

We have used the velocity-map imaging (VMI) technique to measure autoionization dynamics in molecular nitrogen initiated by a train of attosecond pulses. The pump-probe measurements show clear evidence of a crossing between potential energy curves of the highly excited N₂⁺ ion and of the N₂²⁺ ion. It is found that the autoionization becomes energetically allowed when the two nuclei are still very close (∼3 Å), in contrast with observations in other diatomic molecules, and that it can be coherently manipulated by a strong femtosecond infrared pulse.